T/QAS 004-2019 The determination of sulfate in brine by weight method

Scope

Main technical content: 3. Principle: In a neutral or near-acidic solution, SO42- reacts with Ba2+ to form barium sulfate, which has very low solubility. After calcining this precipitate to constant weight and weighing it, the SO42- content can be calculated based on the weight of the barium sulfate. 4. Reagents and materials: Unless otherwise specified, all reagents used in the analysis are of ultra-high purity and meet the requirements of GB/T 6682 for analytical laboratory water. a) Hydrochloric acid: ρ(HCl) = 1.19 g/mL; b) Barium chloride (ultra-high purity); c) Methyl red (ultra-high purity); d) Methyl red indicator (1 g/L); e) Barium chloride solution: Weigh 100.0 g of BaCl2·2H2O, dissolve it in water, and transfer it to a 1000 mL volumetric flask. Dilute with water to the mark and shake well. Filter if necessary. f) Hydrochloric acid (1+1) 5. Instruments and equipment 5.1 Temperature-controlled electric heating plate; 5.2 Analytical balance; 5.3 Muffle furnace. 6. Samples: Store the samples in sealed plastic buckets. 7. Analysis steps Accurately transfer 10 mL of a 10-fold diluted water sample to a 250 mL beaker. Add water to 100–150 mL, add 3 mL of hydrochloric acid (1+1) (f), and use methyl red as an indicator (d). Neutralize until an acidic reaction occurs, then add 1–1.5 mL of hydrochloric acid. Boil under constant stirring. Add 10 mL of barium chloride solution (e) with an excess of 5–10 mL. Continue boiling for 30 minutes and incubate for 4 hours overnight. Filter the precipitate using a slow-quantitative filter paper, then rinse with hot water 2–3 times. Transfer all the precipitate to the filter paper. Wipe the beaker with a small piece of quantitative filter paper and warm water until no Cl- is detected. Transfer the precipitate and filter paper to a previously calcined and weighed porcelain crucible. Place it in a high-temperature furnace. After low-temperature ash removal, gradually increase the temperature to 800–850°

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